WASHINGTON — For most of the last two decades, Republicans such as Rep. Patrick Meehan, who represents a politically competitive district near Philadelphia, have been the odd men out in a House caucus dominated by conservatives such as those aligned with the tea party.

But with Congress' deadlock resulting in the first government shutdown in more than 17 years, Meehan and like-minded colleagues may be the ones who decide how — and when — the standoff ends.

"This whole Congress has been on Cruz control for the last two or three weeks," said Meehan, referring to Sen. Ted Cruz (R-Texas), a tea party favorite. "To a certain extent, you have to let some air out of the balloon."

No matter how legislative standoffs start, they almost always end the same way: One side or the other suffers defections that force its leadership to back down. In any such fight, each side tries to find fault lines in the other's support and see whether pressure can break those fissures open.

In the current battle, conservative Republicans have forced votes on issues they hoped would cause Democratic senators from Republican-majority states to break with Senate Majority Leader Harry Reid (D-Nevada).

Democrats have hoped to divide suburban moderates such as Meehan from hard-line conservatives, who have repeatedly tried to tie money for government agencies to measures aimed at delaying or dismantling President Obama's healthcare law.

On Tuesday, as the shutdown took hold and more Republicans questioned their party's strategy, the gaps on the GOP side were clearly widening. But the party's less conservative members have shown little willingness in the past to fight the right wing. Whether they will now could determine how long the shutdown lasts.

The Republican leadership adopted a new plan to at least buy time — offering three measures that would reopen specific, popular parts of the government, including parks and veterans services.

Democrats quickly circled the wagons against the idea, and the White House threatened a veto.

"This shutdown isn't about spending or deficit or budgets," the president said at the White House. "This shutdown is about rolling back our efforts to provide health insurance to folks who don't have it. This, more than anything else, seems to be what the Republican Party stands for these days."

"People shouldn't have to choose between help for our veterans and cancer research," said Sen. Charles E. Schumer (D-N.Y.). "And we shouldn't have to choose between visiting our national parks or enrolling kids in Head Start."

The GOP's bills, which came up in the House under rules requiring a two-thirds majority to pass, each failed as Democrats voted lopsidedly against them.

A striking degree of Democratic unity has confounded Republican strategies so far. In the Senate, Democrats have remained outwardly unworried about a Republican tack targeting their most politically vulnerable colleagues.

At a House GOP rallyafter an attempt last month to stop the healthcare law, House Majority Leader Eric Cantor (R-Va.) singled out Democratic senators who were up for reelection in 2014 in red states.

"I want to know where Sen. Pryor stands on protecting the middle class from the consequences of this horrific bill," he said, referring to Mark Pryor, the Democratic senator from Arkansas, as Republican lawmakers assembled behind Cantor cheered.

"How about Kay Hagan in North Carolina?" he demanded to more cheers. "What about Mary Landrieu of Louisiana? ... Mark Begich of Alaska?"

Those senators all have stood with their party during the current budget impasse, knowing their earlier votes to pass the healthcare law would be used against them in next year's campaigns regardless of their votes today.

"A group of folks thought that they saw the potential to change some Democrats in the Senate. I was gung-ho to try that. We tried that a couple of times," said Rep. Mario Diaz-Balart (R-Fla.). "I wish it had worked. That unfortunately was not the case. So now we need to take a step back and figure out how we move forward."

On Tuesday, Meehan was one of several who publicly urged the party leadership to pass a simple, short-term spending bill — a continuing resolution, or CR, in legislative jargon — without controversial add-ons, as the Senate did.

"We fought the good fight. Time for a clean CR," said another member of the group, Rep. Scott Rigell of Virginia.

Many hard-core conservatives, who have out-fought the party's more centrist members for years, are skeptical. House Speaker John A. Boehner (R-Ohio) can't afford to capitulate now, they say.

"We have certain times in the calendar year when we have must-pass bills. This is one of them," said Rep. Marlin Stutzman (R-Ind.). "For John Boehner, he goes this far and doesn't walk out with something, it doesn't look good. He has to get something."

Since taking the speaker's job, Boehner has operated in an environment in which his most conservative members have been able to exercise what in effect has been a tea party filibuster in the House.

Republicans hold a 232-to-200 advantage in the chamber. That's the second-largest GOP majority in generations. But because Democrats vote in near unison on high-profile legislation, as few as 16 Republican defections can defeat bills offered by the majority or prevent them from reaching the floor.

Such dissent has most often come from the right. Pressure from conservatives in the House forced Boehner and his leadership colleagues to embrace the conservatives' anti-Obamacare approach to the spending battle.

As the likelihood of a shutdown increased over the weekend, however, the marginalized moderates began to stir.

In a closed-door meeting Saturday,Rep. Charlie Dent (R-Pa.) was the lone member to openly urge the leadership to consider other options. He gathered with a group of like-minded colleagues to discuss whether they could bring pressure to bear from the center.

He and Rep. Peter T. King (R-N.Y.) sought to round up 40 colleagues to insist upon a resolution, enough to provide a cushion in case some got cold feet. King thought they had as many as two dozen committed votes. But on a key procedural vote Monday, Dent and King were the only moderates to vote no.

King and others attributed their failure to members of their party being unwilling to vote publicly against a provision involving insurance premiums for White House and congressional staff members. The bill would have barred the government from paying part of the premiums. Even though most large employers pay part of the premiums for their workers, the "subsidy" for congressional staffers has become a hot-button issue among conservatives.

"If it was a secret ballot, you'd have three-fifths, two-thirds, voting to end it all," King said. "On this one, it was particularly hard because it looked like if you were voting no, you were voting to protect a privileged class. That's the way it would be played in a primary, which is what Ted Cruz people want to do — run primaries against Republicans."

As the standoff drags on, however, the Republican centrists say their ranks will grow and eventually prevail.

"The most important thing for the country is to get a conclusion," said Rep. Frank A. LoBiondo (R-N.J.), whose district posted the third-largest margin of victory for Obama in last year's presidential election of any Republican-held district. "The politics of it are tough, and I get singled out. But I want to do the right thing for the country."

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